As shown in FIG. 12, conventional light source devices for use in liquid crystal projectors comprise a reflector 101 having a paraboloidal reflecting surface and an opening diameter D which is approximately equal to the size W of image display portion 104 of a liquid crystal panel 103. The light from a metal halide lamp or like light source 106 disposed inside the reflector 101 is converted by reflection nearly to parallel rays to irradiate the image display portion 104 of the liquid crystal panel 103.
Unexamined Japanese Patent Publication HEI 2-209093 proposes a liquid crystal projector which comprises a condenser lens disposed on one side of a liquid crystal panel, i.e., on the light source side, and a projection lens disposed on the other side of the panel, i.e., on the screen side, and in which the light passing through the liquid crystal panel is converged on the projection lens.
The above and other publications also disclose a technique wherein a microlens array is provided on the light incident side of the liquid crystal panel for converging the light incident on the panel in corresponding relation to the individual liquid crystal picture elements to improve the substantial opening ratio of the liquid crystal panel.
Further Unexamined Japanese Patent Publication HEI 4-127136 proposes a liquid crystal projector which comprises a light guide tube having a multiplicity of minute apertures for selectively passing therethrough only the vertically incident rays included in a bundle of rays incident on each minute aperture, whereby unnecessary scattering light from the light source is blocked.
On the other hand, Unexamined Japanese Patent Publication HEI 3-196134 proposes an illuminating device which includes a reflector comprising an ellipsoidal mirror and a spherical mirror in combination for guiding light from a light source to outside for efficient use.
With the conventional reflector, however, the metal halide lamp or like light source 106 is not a point light source but a line light source wherein the light-emitting arc is about 5 mm in length L, so that the light reflected from the reflector is not in the form of parallel rays but has a spreading angle .theta.' of about 10 to about 12 deg as indicated in solid lines or broken lines in FIG. 12.
With reference to FIG. 13, the liquid crystal panel 103 includes a liquid crystal material 110 enclosed in a space between two glass panels 107 and 108, and a black matrix 109 in the form of a lattice for preventing light from impinging on a TFT (Thin Film Transistor). One of the glass panels, 108, is provided over its outer surface with an array 111 of microlenses, and the surface of the microlens array 111 is covered with a glass substrate 112.
In the case where the light incident on the liquid crystal panel is parallel rays as indicated in solid lines in FIG. 13, the parallel rays are concentrated at the openings of the black matrix 109 by the action of the microlens array 111 to pass through the pixels of the liquid crystal material 110.
In actuality, however, the light reflected from the reflector 101 has a spreading angle since the light source 106 has the light emission length L as stated above, and the light is concentrated by the array 111 at deflected positions as indicated in broken lines and dot-and-dash lines in FIG. 13, partly impinging on the black matrix 109 and failing to pass through the liquid crystal material. This reduces the apparent opening ratio of the liquid crystal panel to a value lower than is expected.
Accordingly, if the spreading angle of the incident light on the microlens array 111 is within a certain range (generally 8 deg), the light concentrating effect of the array 111 can be expected, whereas if the spreading angle is greater, there arises the problem that the light concentrating action of the lens array 111 produces a reverse effect, failing to achieve an improved light utilization efficiency.
Further with the illuminating device of the above-mentioned publication HEI 3-196134, the reflector of ellipsoidal mirror has two focal positions, and a convex lens is disposed ahead of the second of these positions closer to the liquid crystal panel to obtain parallel rays. Accordingly, the optical path from the light source to the liquid crystal panel has a great length, consequently entailing the problem of making the illuminating device large-sized.